Conventionally, when a cellular modem wishes to access a packet session using for example GPRS, 3G or 4G technology the communication is to a specific network which has an access point, the name of the access point being known as an access point name, APN. This access point name is thus the name of an access point which connects to the packet network. Located at this access point is a Gateway GPRS Support Node, GGSN.
The mobile device reaches the appropriate GGSN through a Serving GPRS support node (SGSN) which is responsible for connecting to packet networks for mobile phones in a particular geographic location.
The protocols for the naming of these concepts, in particular the APN, are contained in the document 3GPP TS 23.003 V12.0.0 (2013-09). “Technical Specification 3rd Generation Partnership Project—Technical Specification Group Core Network and Terminals—Numbering, addressing and identification (Release 12)”, at www.3gpp.org, which teaches the definition and syntax of a number of concepts as used in such technology.
The format of the APN (the name of the network) is as follows. The APN is identified with an APN Operator Identifier, APN-OI, which may be derived from the IMSI as mncMNC.mccMCC.gprs, described by 3GPPTS23.003V12.0.0.0. In this format, “mnc” is a string and MNC is the numeric identifier of the network within a country. Similarly “mcc” is a string and MCC the numeric identifier of the country. An example of an APN OI is mnc058.mcc234.gprs, which is an identifier of the APN (in this case of Manx telecom). This default APN Operatorldentifier is used for roaming situations.
For example, using a general packet radio service, GPRS network, the user of the mobile device (or the software in the device) may select as the network the APN name “eseye.com”. This corresponds to a particular GGSN which represents the link to that network.
The GGSN is identified by a fully qualified domain name FQDN. The FQDN is made up of the APN name followed by the APN-OI so that the resulting FQDN would in the example be eseye.com.mnc058.mcc234.gprs. This FQDN is transmitted by the mobile device to the local SGSN which looks up “eseye.com.mnc058.mcc234.gprs in a local domain name server. The domain name server returns the IP address of the corresponding GGSN and the SGSN then communicates the relevant data with the required GGSN using the returned IP address. In this way, packets from the mobile phone are routed to the correct GGSN where they are connected onwards to a local network or the internet.